In the field of devices for regulating the air flow in a pipe, it is known, in particular from FR-B-2,728,660, to use a calibrating element to adjust the value at which the air flow passing the device is kept substantially constant. A moving flap making it possible to adjust the flow dynamically is mounted with the possibility of pivoting on the calibrating element. The movement of the flap causes the area of an air passage section, delimited by the flap relative to an inner surface of the duct, to vary. The calibrating element is placed in a more or less advanced position in an air duct of the device in order to adjust the air flow, by translating the calibrating element transversely to the longitudinal axis of the duct. In order to ensure sealing of the part of the duct opposite the air passage section, the calibrating element comprises a front face that conceals the duct. When the calibrating element is in its position allowing a maximum flow, that front face tends to protrude from the circumference of the device, such that its implantation in a pipe is delicate.